The maximum image you can project that is still usable is about 20 - 24 inches across. This was tested with an iPod Touch on maximum brightness. If you have another device that is brighter you will be able to make a larger picture.
As many people know, page magnifiers are fresnel lenses. Use google to find out a little more information about them.
Unforunately, I could only find page magnifiers with about an eight inch of plastic attached to them. I assume the manufacturer did this to frevent folding. Try to find page magnifiers that are almost as thin as paper. This thick plastic really made the picture of the output dim and blurry. It will work MUCH better with thinner page magnifiers.
In theory, this should work with a laptop, but when I tried it, it worked just enough to read large text. It would probably be ideal to watch movies. You won't be doing any surfing anytime soon.
One other thing I should mention is that there is no mirrror in my design. Since there is no mirror, all text that is projected will be backwards. If you bounce the iPod image off of a mirror before going into the first fresnel lens, the image will be the right way around.
Thanks for watching!